With conventional x-ray apparatuses for medical applications, a distance from an x-ray source can be manually adjusted. If only a minimum distance between the x-ray source and the patient is selected at the same time as an excessively large dose, this may lead to radiation injury to the skin of the patient.
DE 101 18 183 A1 describes an x-ray device with an apparatus for measuring a distance between an x-ray source and a surface of a patient. The distance is measured from a delay time difference of a laser beam. A thickness of the patient is finally determined from the measured distance on the basis of a previously known distance to a patient support. The device operating parameters are then automatically adjusted on the basis of the determined thickness. The proposed apparatus requires the provision of a light source, which is particularly suited to emitting short light impulses or to emitting amplitude—modulated light. Provision is to be further made for a light receiver, which enables a time resolution in the picosecond, subnanosecond or nanosecond range. The proposed apparatus is generally complex to manufacture. As the device operating parameters and thus the x-ray dose are only adjusted on the basis of the thickness, an inadmissibly high radiation load on the surface of a patient can not always be safely avoided.
US 2005/0013407 A1 describes an x-ray device, in which a laser distance measuring facility is likewise provided to measure a distance between an x-ray source and a patient. In this way, a thickness of the patient to be examined is in turn calculated from the measured distance. A radiation dose is determined as a function of the result thereby achieved. An x-ray dose determined solely on the basis of a thickness of the patient can, in the case of an excessively short distance between the x -ray source and the patient, result in radiation injury to the skin of the patient.